This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 0000041-4 filed in Sweden on Jan. 10, 2000; the entire content of which is hereby incorporated by reference.
The present invention relates to wavelength monitoring of a laser light and more particularly to a method and a device for an integrated wavelength monitor for laser sub-modules.
Fiber-optical transmission is one of the main transfer methods for telecommunication today. Wavelength division multiplexing (WDM) is the preferred method to transfer several channels over an optical fiber. As transmitters Distributed Feedback lasers (DFB-lasers) with precisely controlled wavelengths are typically used for this.
The spacing between individual channels in WDM systems is typically down to 100 GHz corresponding to a spacing of 0.8 nanometer or 0.05% of the wavelength of the laser. To avoid interference between the channels a typical wavelength drift of xc2x10.1 nanometer must be guaranteed. At the system level today a separate unit for monitoring all channels is typically used.
There are several solutions disclosed for obtaining a wavelength monitoring and control for WDM optical transmission systems. U.S. Pat. No. 5,825,792 discloses a compact wavelength monitoring and control assembly for a laser emission source with a distributed feedback (DFB), which comprises an angled Fabry-Perot etalon and two separate photo-detectors, the differential output of which is used in the feedback loop for stabilizing the wavelength of the laser source.
Another U.S. Pat. No. 5,896,201 discloses an optical device for wavelength monitoring and control. The device has an optical element formed as a wedge for dividing a light beam into two differently reflected beams, which beams via a filter reach a first and second photo-detector. On the basis of a difference in wavelength characteristics, the wavelength of the light beam can be monitored according to outputs from the first and second photo-detectors.
Also an international application WO95/20 144 discloses an optical wavelength sensor consisting of a wedge shaped Fabry-Perot etalon which exhibits resonance for different optical wavelengths across its width and an array of detectors that detects the spatial disposition of resonant peaks which occurs.
Still another document U.S. Pat. No. 5,305,330 discloses a system comprising a laser diode and a system to stabilize the wavelength of the laser diode. The system comprises a beam splitter and a diffraction grating for measurement and a number of photo-detectors.
All solutions found so far are rather complex and are more or less difficult to simply implement in a standard laser device. However, a laser with an integrated wavelength monitor would be an attractive component on the market. Therefore there is a demand for a simple compact integrated device for monitoring of the wavelength of a laser device.
A wavelength monitor suitable for integration into a laser semiconductor laser module for fiber optic communication can be made in the following way: An interference filter is deposited directly onto a position sensitive photo detector or mounted directly on top of the detector. The detector device is mounted with an angle behind the laser in the same position as a normal power monitor detector. The electrically derived lateral position of light hitting the Position Sensitive Device provided with the interference filter will be dependent of the wavelength of the incident light and this derived position is used for the wavelength monitoring.
A method for obtaining a wavelength monitor device according to the present invention is set forth by the independent claim 1 and the dependent claims 2-5. Furthermore, a device for controlling the wavelength of a laser source is set forth by the independent claim 6 and further embodiments of the device are set forth by the dependent claims 7-10.